A top World Health Organization
official says a new strain of bird flu in China that has already killed 22 people and spread throughout seven provinces and municipalities is one of the most lethal of its kind to date.
A group of WHO specialists spoke with reporters Wednesday about the H7N9 virus, which has already infected more than 100 people in China. The WHO team arrived late last week for a five-day visit to learn more about the new virus.
According to Keiji Fukuda, the WHO assistant director for health security, at this point, there is still not enough evidence to show the virus can spread easily from human to human.
“When we look at influenza virus this is an unusually dangerous virus for humans…Based on the evidence that we see we think that this virus is more easily transmitted from poultry to humans than H5N1," he said.
The H5N1 strain of bird flu surfaced in 2003. In the past decade, it has swept across three continents and killed more than half of the 622 people it has infected.
WHO and Chinese health officials stress the effort to understand the new strain is still in its early stages.
Liang Wannian of the National Health and Family Planning Commission says just how effective the government’s prevention measures will be remains unclear. He says the extent of the public health risk from the virus remains uncertain, as well.
"There are many unknown factors, including the source of the virus, the mutation of the virus, the pathogenicity, the virulence, the migration, the clinical symptoms and the epidemiological situation of the virus, so we need to study a lot, there are so many things that remained to be studied and learned," he said.
Chinese and WHO scientists all agree that birds infected by the virus, especially poultry, are the likely sources of human infection.
Nancy Cox, director of the Flu Division at the U.S. Centers for Disease Control and Prevention was also part of the WHO team.
"So far, no samples from migratory birds or their habitats have been positive for H7N9," Cox said. "In contrast, samples from chickens, ducks and pigeons have been positive for H7N9 from poultry markets. Also environmental samples taken from poultry markets have been positive."
So far, the majority of deaths and infections from the new strain have occurred in Shanghai. Like many other cities where the virus has cropped up, authorities there have closed down live poultry markets, in response.
Anne Kelson, director of the WHO Flu Research center in Melbourne Australia said the market closings appear to be helping.
“We know that Shanghai rapidly on April 6 closed down their poultry markets in that municipality and it's been very encouraging to see that almost immediately there was a decline in the detection of the new cases and the cases that did occur all occurred in the next week, which you might expect to be within the incubation period of the virus," she noted.
Still, Kelson added that this is no reason to relax. She said close monitoring of the impact the closure of such facilities should continue in the weeks and months to come.
Although Chinese authorities said more than half of those infected have been individuals who had direct contact with poultry or birds, how the remaining number of those infected contracted the virus is less certain.
The government has carried out tens of thousands of tests on birds but only several dozen have turned up positive.
And, in one of the two cases of bird flu in Beijing so far, a young boy contracted the virus, without showing any symptoms of H7N9.